1. Field of the Invention
The present invention relates to a fuel injector for internal combustion engines, more particularly relates to a fuel injector which effectively prevents the occurrence of the undesirable phenomenon of secondary injection after the main injection.
2. Description of the Related Art
In a known fuel injector as disclosed for example in Japanese Unexamined Patent Publication (Kokai) No. 59-206668, when a high voltage is applied to a piezoelectric actuator to stop a fuel injection, the activation is made to extend, a back pressure chamber is made high in pressure, a needle valve is pushed down, the volume of the back pressure chamber enlarges by exactly the amount of lift of the needle valve, and the pressure drops. The pressure pulsation caused at this time is transmitted from a communicating passage to a variable pressure chamber and acts on a piston member to cause the actuator to vibrate and expand and contract. As a result, the pressure pulsation is amplified, and the needle valve opens for a short time once again, causing secondary injection. In extreme cases, several secondary injections occur.